linux-kernel - Re: [PATCH v2 2/6] sched/rt: Optimize select_task_rq

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Date:	Tue, 4 Nov 2014 07:52:37 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"pang.xunlei" <pang.xunlei@...aro.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...il.com>
Subject: Re: [PATCH v2 2/6] sched/rt: Optimize select_task_rq_rt() for
 non-RT curr task

On Tue,  4 Nov 2014 19:13:01 +0800
"pang.xunlei" <pang.xunlei@...aro.org> wrote:

> When selecting the cpu for a waking RT task, if curr is a non-RT
> task which is bound only on this cpu, then we can give it a chance
> to select a different cpu(definitely an idle cpu if existing) for
> the RT task to avoid curr starving.

Absolutely not! An RT task doesn't give a crap if a non RT task is
bound to a CPU or not. We are not going to migrate an RT task to be
nice to a bounded non-RT task.

Migration is not cheap. It causes cache misses and TLB flushes. This is
not something that should be taken lightly.

Nack

-- Steve

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